Abnormal Phenomena Appearing in EHL Contacts

Abstract

In a previous paper the authors showed that when the surface velocity of a body having lower elastic modulus is faster than that of a body having higher elastic modulus, and when the radius of curvature of the former is larger than that of the latter, a deep conical depression (dimple) is produced in the contact surface. This dimple occurs in place of the flat plateau predicted by the point contact elastohydrodynamic lubrication (EHL) theory. In this paper, the effects of surface kinematic conditions on the formation of such abnormal phenomena, which cannot be predicted by the present EHL theory, are investigated under rolling/sliding conditions using the optical interferometry technique. Transient behavior of the dimple caused by a groove passing through the EHL conjunction is also discussed based on direct observations. It has been found that the dimple occurs when the lubricating oil in the contact area is composed of solidified and unsolidified parts, and the dimple itself corresponds to the solidified part. On the basis of this finding, it has been asserted that the establishment of a new EHL theory is needed.

Non-classical Elastohydrodynamic Lubricating Film Shape Under Large Slide-roll Ratios

“…The Kaneta dimple, which cannot be explained by the classical EHL theory, was numerically studied by Yang et al [15][16][17] using the thermal viscosity wedge concept. Their numerical results matched the measurements of Kaneta et al [13,14] well, and they also proved that the dimple could only be formed under pure glass-disc sliding. Hence, Yang et al claimed that the thermal viscosity wedge is the most reasonable explanation for the Kaneta dimple.…”

“…In the 1990s, Kaneta et al [13,14] produced highquality images of a dimple-shaped EHL contact in an optical EHL test rig. They reported that a deep central dimple occurred with pure glass-disc sliding, but not with pure ball sliding, even though both cases were the same kinematically (pure sliding).…”

EHL Film Thickness Limitation Theory Under a Limiting Shear Stress

“…Secondly, they showed abnormal interferograms of their experimental contacts compared with conventional ones, but were not aware that their observed phenomena may be the samc with the earlier findings by Lee et al (1973) for the similar case, which showed anomalous results of film thickness and its vrrricrtion with load in their experiment compared with conventional EHL theories indicating severe film collapse at relatively heavy loads. Surprisingly, Kaneta et al (1996) measured the film thickness higher than conventional EHL theory prediction indicating dimples of their contacts. Their measurement should be rather abnormal, since simple sliding normally results in reduced film thickness compared with conventional EHL theories as measured by Lce et al (1973).…”

From Continuous to Molecular Scale in Modelling Elastohydrodynamic Lubrication: Nanoscale Surface Slip Effects on Film Thickness and Friction

“…11 Film thickness profiles obtained for different SRR values and from classical and composite (including nanoscale slip) models zone greatly changes. Even with moderate SRR values (for instance SRR = 0.2), the curvature in the film thickness profile changes sign, as experimentally observed in the literature and referred to as dimple occurrence [33,34]. On the numerical side, Ehret at al.…”